Removing glue left by new windows

Hello everybody - I was asked to clean a new house with new modern double glazed windows
However the glue from the plastic sheet on the new windows was still
On the window
What’s best way to remove this stubborn glue ?
Thanks

razor blade, goo gone, heat gun

You can also use Oil Flo from Titan (they sell it here if you don’t have it). Or graffiti remover, Goof Off. Wool it, Bronze wool. But a razor blade scraper might work the fastest.

I absolutely agree with the other posts, but if the glue is fairly new, not thick or sun cooked. Just to keep it from resicking as you blade it try Dawn with water in a spray bottle to keep it wet. I’ve had this work, it’s cheap, and you will find out quick if it don’t work. Then bring out the big guns.